1. Field of the Invention
The present invention relates to an image forming apparatus which performs calibration for maintaining the image quality.
2. Description of the Related Art
The image quality of an image forming apparatus varies depending on its use environment and use condition. The image quality also varies depending on the type of printing medium to be used. Therefore it is necessary to change the image conversion conditions and image forming conditions depending on the environment and use condition (Japanese Patent Laid-Open No. 07-261479). In some cases, image conversion conditions and image forming conditions need to be added according to the type of printing medium to be used (Japanese Patent Laid-Open No. 08-287217).
The invention in Japanese Patent Laid-Open No. 07-261479 assumes that a specific type of printing medium (to be referred to as the first printing medium) is used for calibration each time. If the first printing medium runs out, no calibration can be performed. Even in the invention of Japanese Patent Laid-Open No. 08-287217, performing calibration for an added arbitrary type of printing medium (to be referred to as the second printing medium) requires a printing medium of the same type to be prepared each time. This is because the calibration aims to maintain the gradation characteristic for the added second printing medium. If calibration is performed using the second printing medium of a type different from the first printing medium, for example, the amount of applied toner may become insufficient or exceed a permissible range designed for the image formation apparatus. This means that the image quality cannot be maintained. It would be convenient for the operator if calibration for the first printing medium can be performed using the second printing medium. For example, the use of an OHT (Overhead Transparency) sheet is designated for calibration for maintaining the gradation characteristic for the OHT sheet. However, making plain paper usable for calibration to maintain the gradation characteristic for the OHT sheet brings about significant advantages to the operator. It would be especially convenient if the second printing medium as another type can be additionally registered without using the first printing medium designated in advance by the manufacturer or the like.